(1)令x1,x2是f(x)定义域上的两个数,并且 x1>x2>1;则 f(x1)-f(x2)=2(x1-x2)+(1/x1)-(1/x2)=2(x1-x2)+(x2-x1)/(x1x2)=(x1-x2)[2-1/(x1x2)]因为x1>x2>1,所以 x1-x2>0;x1x2>1即2-1/(x1x2)》0；故f(x1)>f(x2)又因为x1>x2,...